The present invention relates to the general field of systems used for exhausting gas from a gas turbine, in particular for aviation by-pass gas turbines, i.e. gas turbines having at least two distinct streams flowing therethrough (a primary or “core” stream and a secondary or “by-pass” stream). The invention relates more particularly to exhaust systems for such gas turbines having a primary nozzle and a secondary nozzle that are designed to be placed concentrically at the outlet from such a gas turbine.
FIG. 1 is a fragmentary and diagrammatic view of an exhaust system for an aeroengine delivering separate streams and comprising a primary nozzle 10 placed inside a secondary nozzle 20 made up of two portions, namely an upstream secondary nozzle 21 and a downstream secondary nozzle 22 (where the terms “upstream” and “downstream” are used herein relative to the flow direction of the stream of gas through the engine). A central body or “plug” 30 is present inside the primary nozzle 10.
The primary nozzle 10 is designed to be connected to the exhaust casing of the engine via a radial flange 11, while the secondary nozzle 20 is attached by its upstream portion 21 to the primary nozzle 10 by means of supports 12. With this architecture, the secondary nozzle 20 is supported entirely by the primary nozzle 10, which is subjected via its radial flange 11 to all of the mechanical loads that pass through both nozzles.
Consequently, the primary nozzle 10, which corresponds to the structural portion of the exhaust system that needs to support the secondary nozzle and to withstand mechanical and thermal loads, must be made of a refractory material that is strong enough to withstand all these stresses. The primary nozzle is typically made of a metallic material such as Inconel®.
That type of design for an exhaust system presents the drawback of subjecting the primary nozzle to high mechanical loads, thereby reducing its lifetime and increasing expensive maintenance costs.
Furthermore, that exhaust system architecture presents relatively high overall weight cantilevered out inside the engine, thereby increasing the mechanical loading on the flange of the nozzle exhaust casing.